Turbine and other rotary engines often have several wholly or partly independent means of interrupting the fuel flow in order to shut down the engine. A first means of shutdown is a normal shutdown means, another one may be an automatic overspeed shutdown means, and yet another may be an especially fast (emergency) shutdown means needed in case part of the engine breaks. It is generally easy to arrange for consolidation of several of these means for shutdown with some form of electronic or other logic device to control one or more solenoid type fuel shut-off valves.
However, there is also a need to ensure that one or more means can operate independently of these electronic or other logic devices. Also, the need for a fast (emergency) shutdown is normally incompatible with the need to have a permanent shutdown command if both are implemented via a single solenoid fuel shut-off valve. There is therefore a requirement in the industry for a solution to this particular problem.